Today I read somethign regarding the Dagor Dagorath and in one version it is stated that Turin will become a Valar, or even before the last battle

Quote

and so were all their sorrows and stains washed away, and they dwelt as shining Valar among the blessed ones, and now the love of that brother and sister is very fair; but Turambar indeed shall stand beside FionwŰ in the Great wrack, and Melko and his drakes shall curse the sword of Mormakil."

and in other versions he will slay Ancalagon (but wasn┤t he earlier killed by Earendil anyway?) and then left the circles of the word and didn┤t become a Valar.

Quote

... unless the prophecy of Andreth the Wise-woman should prove true, that T˙rin in the Last Battle should return from the Dead, and before he left the Circles of the World for ever should challenge the Great Dragon of Morgoth, Ancalagon the Black and deal him the death-stroke. Note 17; The Problem of Ros; HoME 12 The Peoples of Middle Earth

What was Tolkiens final word on that and what do you think? Did he become a Valar or left he the circles of the world?

The idea of humans becoming Valar doesn't fit with Tolkien's later writings. I would imagine that part was abandoned. The later prophecy of the Dagor Dagorath stated that Turin will return for the final battle with Morgoth. He will come from beyond the Circles of the World, from wherever Men go after they die. But as all this comes from the History of Middle-earth series, there's no telling what Tolkien would have kept or rejected if he'd published those writings himself.

I didn't recall the part about Ancalagon returning. That was probably meant to be similar to the Ragnarok stories of Norse myth where Thor battles the world-serpent Jormungand. Not sure how Ancalagon would return from death as well. Spirit freed from the Void by Morgoth?

The note to the problem of Ros is the last word, but as you've written, it introduces a massive overhaul of the legend of the War of Wrath, and takes away Earendil's exploit. Ancalagon becomes the Midgardsormer in a future Ragnarok, rather than the first and greatest of winged dragons; but at least the element of the most powerful Ainu being slain be a mere mortal is eradicated - and that in a version which is supposed to be a Mannish tradition! Also, once this vision is attributed to Andreth, this supports Christopher Tolkien's decision to altogether omit the Second Prophecy of Mandos from the published Silmarillion - a decision which Voronwe lamented in Arda Reconstructed, and in this_thread (he attributes CT's decision to the end of the Valaquenta, and takes issue with it). I've made this point in my reponse (one of the last in that thread) to him - but if you have the time, reading the whole discussion should be very interesting.One point, however, is that is Ancalagon the Black will appear in the Last Battle - Gandalf's words reagrding him to Frodo in The Shadow of the Past seem wrong, as they imply he was the greatest dragon in the (then) history, not a present or future menace.

The description of Turambar and Nienori's fate in The Book of Lost Tales is very interesting (I've commented about it in the thread linked to above), but I must say that despite the phrase "as shining Valar", I have always assumed that they were no more than counted among the sons of the Valar, Tolkien's early concept of the Maiar. This was clearly rejected in later versions; but I suppose that without it, tolkien would never have come to the idea that Turin would become Melkor's Bane - a fate which I think hardly makes sense in the later story. But it took Tolkien half a century to (maybe) discard it altogether, and he never wrote any alternative version of the Last Battle. One hint in a footnote doesn't mean that he even had any alternative vision, or even conception of it.

I never saw Turin slaying Melkor as a problem or an unlikely event within the myth
[In reply to]

Can't Post

beause I do not think it is ever written that he alone slays Melkor, more that he gives him his death stroke after he is substantially weakened and/or preoccupied fighting another or others. Similar to how Eowyn finished off the Witch King.

It seems to be fitting and fated that this happens given the singular way Melkor as Morgoth cursed Hurin and his family.